000
FXUS63 KMKX 121108
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
508 AM CST Tue Dec 12 2017
.UPDATE...
Skies clearing west areas, with mostly cloudy skies north and
east areas. gradual clearing from the west, but clouds should
remain especially north of Milwaukee into mid/late morning. Also a
few flurries.
Latest 06Z NAM and GFS are similar with snow amounts for Wednesday
system. Appears advisory headlines most likely. NCEP winter watch
collaborator only in the 5 to 10% range for warning amounts Fond
du lac, Sheboygan and Milwaukee areas. Watch should be in the 50%
range or higher.
&&
.AVIATION(12Z TAFS)...
Skies clearing west areas, with cigs 3-4 thsdft north and east
areas. gradual clearing from the west, but clouds should remain
especially north of Milwaukee into mid/late morning. Also a few
flurries.
North to northwest winds will remain quite gusty through the
morning and begin to diminish this afternoon. finally settling
down with sunset tomorrow evening.
Mid clouds will move in this evening, then lower to MVFR in
light snow late tonight.
&&
.PREV DISCUSSION... (Issued 245 AM CST Tue Dec 12 2017)
SHORT TERM...
Today and Tonight...Forecast Confidence is Medium...
The upper trough over the Great Lakes moves off to the east as a
shortwave approaches the Upper Mississippi valley area by sunrise
Wednesday. 700 mb downward motion today, then upward motion by
midnight as upper leveldivergence increases ahead of the
shortwave. Mid level moisture increases from the west tonight,
with 700 mb layers saturating by midnight.
Low level moisture lingers far east areas, especially north of
Milwaukee. This area finally dries this afternoon. As a result
some flurries could linger vicinity Sheboygan and Port Washington
into mid morning.
850 mbRH increases late tonight, so we could see some light snow
during the early morning hours.
Look for gusty northwest winds to remain through the morning,
then diminish during the afternoon as a weak ridge moves across
the Mid Mississippi Valley. Wind chills into mid morning will be
around zero or a few degrees below zero. Temperatures will drop
this evening, then slowly rise late tonight.
LONG TERM...
Wednesday and Wednesday night...Forecast confidence is medium.
A Pacific wave now breaking along the British Columbia coast will
crest the expansive western ridge later today, before dropping
southeast from the Canadian Prairies into the Upper Midwest and mid
Mississippi valley on Wednesday and Wednesday night. The wave will
escort surface low pressure as it develops southeastward from
southern Minnesota into northern Illinois. A strong push of focused
warm/moist advection will accompany the wave, bringing a moderate to
strong mid-level frontogenesis response and robust lift within the
dendritic growth zone. Models have responded to this increased
moisture and lift with greater QPF focused within a narrow zone of
ascent located along and northeast of the surface low track. This
increases our concern that a snow band may set up across some
portion of our area producing at least moderate snowfall rates along
with fast accumulations. Current model solutions place this "sweet
spot" across our east and northeast (say, from Milwaukee north and
northwest towards Fond du Lac and Sheboygan), where 3-6" of
accumulation would be possible. Amounts would then sharply decrease
southwest of those areas, with areas west of Madison perhaps seeing
very little measurable snow. Keep in mind that only a small change
in the surface low track could shift the location of this heavier
snow band, so the amounts and locations mentioned above aren`t
written in stone. Keep up with the forecast. This could be one of
those situations where some areas get a rapid multi-inch
accumulation while others nearby see much less. A winter weather
headline (advisory or warning) may be necessary for portions of our
area later today, but per collaboration with neighboring offices
decided to hold off on this decision allowing for additional model
information to better iron out the best location for any possible
headline. The key message is that some portion of our area could see
an impactful snowfall during the late morning to afternoon hours on
Wednesday. Our secondary concern is the possibility of a little
freezing drizzle on the back side of the system mainly for areas
along and southwest of Madison during the late morning to afternoon.
Lows Wednesday night will drop off into the teens to upper single
digits, and potentially even colder for areas with the deeper
snowpack.
Thursday through Tuesday...Forecast confidence is medium.
Northwest flow prevails for Thursday and Friday, with a few weak
perturbations trapped within the meanflow. The stronger of these
waves could produce some light snow on Friday, with some areas
perhaps seeing a dusting or few tenths of an inch of accumulation.
Impacts from this appear minimal at this point. Uncertainty
remains regarding a weather system next weekend. The GFS maintains
its farther north track, resulting in warmer temperatures with
the bulk of any precipitation off to our north. The ECMWF provides
a colder and slower solution with the surface low tracking to our
south. This solution could bring a little light snow to our area
over the weekend, but amounts have decreased from the previous
model solutions. Not enough agreement to lean on any particular
model at this point, so will defer to the blended model solution
until things become clearer.
AVIATION(09Z TAFS)...
Skies clearing west areas, with cigs 3-4 thsdft north and east
areas. gradual clearing from the west, but clouds should remain
especially north of Milwaukee into mid/late morning. Also a few
flurries.
North to northwest winds will remain quite gusty through the
morning and begin to diminish this afternoon. finally settling
down with sunset tomorrow evening.
Mid clouds will move in this evening, then lower to MVFR in
possible light snow late tonight.
MARINE...
Hazardous marine conditions with northwest gales through mid/late
morning. In addition to the winds, a fair amount of wave action
is expected as well, especially toward open waters. Also some
freezing spray.
GaleWarning continues for the nearshore waters until 10 am.
A Small Craft Advisory will be necessary following the GaleWarning for continued gusty winds and high waves into the
afternoon.
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...GaleWarning until 10 AM CST this morning for LMZ643>646.
&&
$$
Update...Hentz
Today/Tonight and Aviation/Marine...Hentz
Wednesday THROUGH Monday...SPM